WO1993006650A1

WO1993006650A1 - Single-stage electrical conversion device

Info

Publication number: WO1993006650A1
Application number: PCT/EP1992/002218
Authority: WO
Inventors: Paolo Tenti
Original assignee: Paolo Tenti
Priority date: 1991-09-27
Filing date: 1992-09-24
Publication date: 1993-04-01
Also published as: IT1257981B; ITPD910177A1; ITPD910177A0

Abstract

Single-stage electrical conversion device, characterized in that it comprises rectification means (3) which are supplied by the mains (1) and are provided with filtering means (2) which control a voltage at the terminals (E, D) of switching means (4, 5). Resonating means (6, 7) are furthermore provided and are interposed between the switching means (4, 5) and termination means (A, B).

Description

SINGLE-STAGE ELECTRICAL CONVERSION DEVICE Technical Field

The present invention relates to a single-stage electrical conversion device.

Background Art

In countless applications which have any kind of converter in input, either of the AC/AC type or of the AC/DC type, so far the performance of these converters has been considered almost exclusively on the load side, with no analysis at all for spurious responses on the supply side.

In practice, these converters currently tend to introduce on the supply line higher-order current harmonics which tend to affect both other devices connected to the same supply network and measurement instruments used to detect consumption and thus to calculate the power used.

It is furthermore always necessary to control the energy aspect, especially in circuits which operate as power supplies for fluorescent lamps, switching power supplies for household appliances and the like. Disclosure of the Invention

The aim of the present invention is to eliminate or substantially reduce the problems described above by providing a single-stage electrical conversion device which eliminates the low-frequency harmonic components sent on the supply line.

Within the scope of the described aim, an object of the present invention is to provide a device which allows a wide adjustment range of the power transferred to the load. Another object of the present invention is to provide a device which eliminates steep current and .voltage fronts during switching.

Not least object of the present invention is to provide a device which is highly reliable, relatively easy to manufacture and at competitive costs. This aim, the objects mentioned and others which will become apparent are achieved by a single-stage electrical conversion device, characterized in that it comprises mains- supplied rectification means which are provided with filtering means which control a voltage at the terminals of switching means, resonating means being provided and interposed between said switching means and termination means.

Brief description of the drawings

Further characteristics and advantages of the invention will become apparent from the description of a preferred but not exclusive embodiment of a single-stage electrical conversion device according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: figure 1 is a general diagram of a conversion device according to the invention; figures 2a, 2b, 2c, 2d and 2e are further embodiments of the circuit shown in figure 1; figures 3a, 3b, 3c and 3d are Cartesian plots of the typical behavior of some values of the device according to the invention during its operation; figures 4a and 4b are Cartesian plots of the typical behavior of some values ahead of the device according to the invention during its operation. Ways of carrying out the invention

With reference to figure 1, a single-stage electrical conversion device comprises filtering means which are input- connected to a mains power supply 1 and are output-connected to rectification means. Said rectification means generate a voltage which is sent to the terminals of switching means.

Resonating means are furthermore provided and interposed between the switching means and termination means.

The filtering means comprise a first inductor 2 which is arranged on a positive (or negative) branch of the mains power supply 1 or after the rectification system, or both.

The rectification means comprise a diode bridge 3 which is composed of four diodes 3a, 3b, 3c and 3d; on one diagonal of said bridge, an output terminal of the first inductor 2 is connected on one side and a negative terminal of the mains supply 1 is connected on the other side. The diode bridge 3 has output terminals on its other diagonal.

It would also be possible to use other rectification means, such as for example a dual half-wave rectifier with center-tap transformer. The switching means comprise a parallel arrangement which is constituted by an electronic switch 4 and by a power diode 5. The electronic switch 4 can comprise a MOSFET transistor, as shown in figure 1, or a bipolar transistor or the like. The resonating means comprise a capacitor 6 and a second inductor 7 placed in series.

Various termination means can be connected to the output terminals A and B of the device according to the invention; said means can comprise (figure 2a) a load, represented by a lamp 8 and by a starter 9, or (figure 2b) a transformer 10 on whose output terminals a rectifier or diode bridge 11 is connected, a load 12 being connected to the output terminals of said rectifier or bridge 11, or (figure 2c) a rectifier or diode bridge 13 on whose output terminals a load 14 is connected.

In the circuit of figure 1 it is possible to interpose

(figure 2d) a filter which comprises a capacitor 15 and an inductor 16 and/or 16a respectively between the terminals C and E or in series to the capacitor 15 between points C and

D.

Between the terminals C and D of the circuit of figure

1 it is possible to interpose (figure 2d) a filter which comprises a capacitor 15 and — possibly — an inductor 16a, whereas an inductor 16 can be interposed between the terminals C and E.

Figure 2e illustrates a further variation, wherein the resonating inductor is replaced with a mutual inductor 17a,

17b and 17c whose function is to draw, during part of the mains cycle, power from the resonating circuit and transfer it, by means of the diodes 18a and 18b, to the capacitor 19. The capacitor 19 returns, at appropriate times, said power to the resonating circuit by means of the inductor 20 and the diode 21. With this configuration, the ripples of the current of the load 22 and of the mains current are reduced.

Naturally, the dual half-wave rectifier constituted by the windings 17a and 17b and by the diodes 18a and 18b can be replaced with other rectifier layouts. Figures 3a, 3b, 3c and 3d plot the typical behaviors of some values in the device according to the invention during high-frequency operation as a function of time.

Assume ic is the current which flows on the second inductor 7, i^ is the current in output from the rectifier 3, uc is the voltage across the capacitor 6, u^ is the voltage of the switch 4, i_τ is the current which flows in the branch which contains the switch 4 and the diode 5, ug is the supply voltage, ig is the line current and UR is the voltage in output from the rectifier 3, and consider their behavior as a function of time.

During the period T_on for which the switch is closed, which is equal to the interval TQ-T2 in figures 3a-3d:

— the resonating circuit composed of the capacitor 6 and of the inductor 7 oscillates, i.e. i_c and Uc evolve with a sinusoidal pattern which is damped by the resonance time constant;

— the current i^, which is indicated in broken lines in figure 3a and whose amplitude coincides with the line current ig, rises in an almost linear manner, whereas the voltage ug remains practically constant during all of the period T_orι and is entirely applied to the inductor 2;

— the switch current ir performs a positive half- oscillation, in the interval T_Q-T_I^, and then reverses, flowing in the diode 5, in the interval Tχ-T2. The switch 4 is closed with an appropriate control command at the time TQ. This step ends when the current ij in the diode 5 ceases, i.e. at the time T2.

During the switch opening time ₀ff, which is equal to the interval T2-T₃ in figures 3a-3d, the current 1R flows in the resonating circuit. Power is correspondingly transferred from the rectifier 3 to the resonating circuit, which is constituted by the capacitor 6 and by the inductor 7, and from the termination element C, and the voltage uc rises, while the current i^ decreases. The voltage across the switch 4 is thus equal to the voltage u plus the load voltage. This step ends upon the subsequent closure of the switch 4.

It is evident that whereas the period T_on depends exclusively on the parameters of the resonating circuit 6/7 and on the operating conditions, and thus cannot be controlled except during design, the time T₀ff can be controlled in order to obtain an adjustment of the power transferred to the load.

It is possible to define a period of operation of the switch 4 as:

T = T_on + T₀ff and the duty cycle as: d = T_on/T

It should be furthermore noted that the switchings of the switch 4 are also non-dissipative. In fact:

— closure of the switch 4 occurs at almost nil current, since the rise of the current during said closure is limited by the presence of the inductors 2 and 7;

— opening of the switch 4 is performed during the conduction step of the diode 5, and thus occurs at almost nil voltage;

— the waveform of the current in the diode 5 is sinusoidal, with scarcely steep fronts, and thus the voltage during forward recovery is limited; and - the reverse recovery current of the diode is limited by the inductors 2 and 7.

Figures 4a-4b illustrate low-frequency operation on the side of the mains power supply 1.

The typical waveforms on the mains side are illustrated therein; the voltage UR is the voltage present at the input terminals of the rectifier 3; the voltage ug and the current ig are respectively the voltage, assumed to be purely sinusoidal for the sake of simplicity in illustration, and the current of the mains supply 1. It should be noted that, differently from typical behaviors of conventional purely capacitive rectifier systems, the behavior of the mains current approximates a sinusoid which is in phase with the mains voltage. Distortion of the current ig naturally depends on the inductance value of the inductor 2.

It should be stressed that the purely sinusoidal behavior obtained is advantageously achieved with no modulation of the duty cycle, contrary to what is described in the prior literature. Conveniently, the device according to the invention can be integrated easily and at competitive costs, since it has a single electronic switch and a power diode, contrary to what other known power supply circuits have.

Practical tests have shown that the device according to the invention achieves the intended aim and objects, advantageously eliminating current harmonics reflected onto the power supply network and furthermore allowing to adjust the power transferred from the network to the load.

The device according to the invention thus conceived is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept. The device according to the invention can in fact be manu actured dually with respect to the above described embodiments. All the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials employed, as well as the dimensions, may be any according to the requirements.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identi ied by way of example by such reference signs.

Claims

1. Single-stage electrical conversion device, characterized in that it comprises mains-supplied rectification means (3) provided with filtering means (2) which control a voltage at the terminals (E,D) of switching means (4,5), resonating means (6,7) being provided and interposed between said switching means (4,5) and termination means (A,B).

2. Device according to claim l, characterized in that said filtering means comprise a first inductor (2) which is arranged on a branch of the mains power supply (1) or after the rectifier (3), or both.

3. Device according to the preceding claims, characterized in that said rectification means comprise a diode bridge (3) with an output terminal of said first inductor (2) connected to one side of a diagonal of said diode bridge (3) and a negative branch of the mains power supply (1) is connected to the other side, said diode bridge (3) having output terminals (C,D) at its other diagonal.

4. Device according to one or more of the preceding claims, characterized in that said switching means comprise a parallel arrangement constituted by an electronic switch (4) and a power diode (5) .

5. Device according to one or more of the preceding claims, characterized in that said resonating means comprise a series arrangement of a capacitor (6) and of a second inductor (7) .

6. Device according to one or more of the preceding claims, characterized in that said electronic switch (4) comprises a MOSFET transistor or a bipolar transistor or an IGBT (insulated gate bipolar transistor) or another equivalent device.

7. Device according to claim 1, characterized in that said termination means comprise a load (8) .

8. Device according to claim 1, characterized in that said termination means comprise a transformer (10) on whose output terminals a rectifier (11) , able to supply a load (12), is connected.

9. Device according to claim 1, characterized in that said termination means comprise a rectifier (13) able to supply a load (14).

10. Device according to claim 1, characterized in that it comprises a capacitive filter (15) which is interposed between said rectifier (3) and said switching means (4,5).

11. Device according to claim 10, characterized in that it comprises an inductor (16) which is arranged between said capacitive filter and said switching means or in series to said capacitive filter (15).

12. Device according to claims 1 and 10, characterized in that it comprises an inductor (20) and a diode (21) arranged in series between said capacitive filter (19) and said switching means and furthermore in that it comprises a mutual inductor (17a, 17b,17c) arranged in series to the load (22).

13. Device according to claim 12, characterized in that it comprises a rectification means (18a,18b) which is connected to the output of said mutual inductor (17b,17c) in order to transfer power to the capacitor (19) of the capacitive filter.

14. Device according to one or more of the preceding claims, characterized in that said device has a dual execution with respect to claims 1 to 11.